1. Field of the Invention
The present invention generally relates to a nuclear reactor internal structure and more specifically to an internal structure and coolant supply structure of a pressurized water reactor by which flow of coolant in the reactor can be rectified.
2. Description of the Related Art
As a conventional technology relating to a nuclear reactor internal structure by which flow of coolant can be rectified, there are known the following patent documents, that is, the Japanese patent publication Nos. 2999124 (pages 2 and 3, FIGS. 3 and 4) and 3193532 (pages 3 and 4, FIGS. 2 and 3) and the Japanese laid-open patent application Hei 8-62372 (page 2, FIG. 4). In these documents, a connecting plate having its outer periphery formed in a circular shape is disclosed. A basic structure of a reactor vessel of a pressurized water reactor in which such a connecting plate is used is shown here in FIG. 19. In FIG. 19, coolant 1 flows in through a coolant inlet nozzle 3 that is integrally formed with a reactor vessel 2 and flows down as a downflow 6 in a downflow path portion or a downcomer portion 5 formed in an annular shape between the reactor vessel 2 and a reactor core tank 4. The downflow 6 passes through a radial key portion 7 provided having a key groove structure for positioning a lower portion of the reactor core tank 4 relative to the reactor vessel 2 and enters a lower plenum 8. Then, the coolant 1 is directed upward by a spherical inner surface 9 of the lower plenum 8 to pass through a lower connecting plate 10, upper connecting plate 11, lower reactor core supporting plate 12, etc. and flows in a reactor core 13.
An upflow 14 that has entered the reactor core 13 absorbs heat generated by a fuel assembly 15 in the reactor core 13 to be heated to a high temperature and passes through a coolant outlet nozzle 17 in an upper plenum 16 to flow out to a steam generator (not shown). Then, the coolant 1 transfers the heat to cooled water in the steam generator to heat and boil it and is again sent toward the nuclear reactor by a coolant circulating pump (not shown) to be returned into the reactor vessel 2 through the coolant inlet nozzle 3. In FIG. 19, numeral 4a designates a lower reactor core plate that supports the fuel assembly 15, numeral 19 a lower reactor core strut, numeral 20 a falling shock absorbing plate and numeral 20a an instrument guide pipe.
The mode of arrangement of the coolant inlet nozzle 3 and coolant outlet nozzle 17 is shown in FIG. 20 being a cross sectional view taken on line IIX—IIX of FIG. 19.
In FIG. 20, for convenience of description, an axis relative to which the coolant outlet nozzles 17 of an upper pair are positioned in symmetry to each other is defined as an angle 0° axis and each axis is designated by the angle counted counter-clockwise. Thus, on the opposite side of the coolant outlet nozzles 17 of the upper pair, the coolant outlet nozzles 17 of another pair are positioned in symmetry relative to the 180′ axis. Also, the coolant inlet nozzles 3 of a pair are positioned in symmetry relative to the 90° axis and the coolant inlet nozzles 3 of another pair are positioned in symmetry relative to the 270′ axis.
On the other hand, the mode of arrangement of the radial key portion 7 of a lower portion of the downcomer portion 5 is shown in FIG. 21 being a cross sectional view taken on line IX—IX of FIG. 19. As shown in FIG. 21, six of the radial key portions 7 are arranged at positions of 60° intervals starting from the reference of the 0° axis in the downcomer portion 5.
In FIG. 22 being a cross sectional view taken on line X—X of FIG. 19, the lower connecting plate 10 arranged in the lower plenum 8 is a circular plate-like member having its outer circumferential periphery formed in a ring shape as a ring portion 21. A circular inside portion of the ring portion 21 is formed by a rim portion 23 having a multiplicity of small holes 22 into which the instrument guide pipes 20a are inserted. The rim portion 23 spreads in a mesh form so as to surround and support these small holes 22 and connects to the ring portion 21.
Both of FIGS. 23(a) and (b) are views of the lower connecting plate 10 as seen from below in the lower plenum 8 and show the state of flow of the coolant 1 on the lower side of the lower connecting plate 10 in the lower plenum 8.
The coolant 1 flowing into the reactor through the coolant inlet nozzles 3 of one pair joins together so that the flow velocity thereof becomes faster and flows down in the downcomer portion 5, wherein a portion of the coolant 1 disperses in the circumferential direction in the downcomer portion 5.
Thus, the flow of the coolant 1 can be divided into two portions, that is, on one hand, a main flow 26, 27, as shown in FIG. 23(b), in which the coolant 1 flows down in the downcomer portion 5 substantially perpendicularly from the coolant inlet nozzle 3 and flows in toward a central portion of the lower plenum 8 through between the ring portion 21 of the lower connecting plate 10 and the inner surface 9 of the lower plenum 8 and, on the other hand, a dispersing flow in which flow of the coolant 1 disperses in the circumferential direction in the downcomer portion 5.
A portion of the dispersing flow, while it goes down, impinges on the radial key portion 7 to thereby form a separating flow 28, 29, as shown in FIG. 23(a), on both sides of the radial key portion 7 and this separating flow 28, 29 flows in toward the central portion of the lower plenum likewise through between the lower connecting plate 10 and the inner surface 9 of the lower plenum 8.
FIG. 23(a) shows the state of the separating flow 28, 29 on the lower side of the lower connecting plate 10 and the state of generation of small vortices, that is, object-downstream separating vortices caused by the separating flow 28, 29 around the radial key portion 7. Here, as the coolant 1 flows in the state of turbulence of a high Reynolds number, by the characteristic of the turbulence, the flow of the coolant 1 is in the state of a random velocity in which the small vortices repeat appearance/disappearance in the flow. If the impinging flow and the separating flow join together, while a further complicated flow is generated, there is also considered a possibility that the separating flow is stabilized or rather promoted or the small vortices are stabilized or rather promoted according to the mode of the joining.
FIG. 23(b) shows the state in which the main flow 26, 27 coming in from the 90° axis side and the 270° axis side, respectively, impinges on the separating flow around the central portion of the falling shock absorbing plate 20 to become the impinging flow separated into the 0° axis side and the 180° axis side and flows toward around the radial key portion 7. The separation is enlarged by the main flow 26, 27 coming in around the radial key portion 7 and the separating vortices are promoted so that the size of the separating vortices themselves becomes larger.
With respect to each pair of the coolant inlet nozzle 3 and the coolant outlet nozzle 17, adjacent to each other, the steam generator and the coolant pump, respectively, are connected to them, so that four loops of a primary cooling system are formed, wherein each of the coolant pumps generally has the same discharge rate.
FIG. 24 is a development view for explaining the structure of the downcomer portion 5, wherein an outer circumferential surface of the reactor core tank 4 of a cylindrical shape is developed into a flat plane.
On the outer circumferential surface of the reactor core tank 4, a thermal insulator 319 of a substantially rectangular shape is provided so as to slightly protrude into the downcomer portion 5. Between two adjacent thermal insulators 319, an inter-thermal insulator flow path 321, 322 of a substantially equal width is formed so that the coolant 1 flows down along this inter-thermal insulator flow path 321, 322.
Also, below the thermal insulator 319, there is provided a radial connection portion 7′ of a substantially rectangular shape having a key groove structure for positioning the lower portion of the reactor core tank 4 relative to the reactor vessel 2 and by this radial connection portion 7′, the reactor core tank 4 is connected to the reactor vessel 2 in the downcomer portion 5.
As shown in FIG. 19, the coolant 1 flows in from the coolant inlet nozzle 3 and flows down in the downcomer portion 5 as the downflow 6. In the downcomer portion 5, as shown in FIG. 24, the coolant 1 mainly flows down through the inter-thermal insulator flow path 321, 322 and enters the lower plenum 8 through between the radial connection portions 7′.
Here, the inter-thermal insulator flow path 321 is provided below the coolant inlet nozzle 3 and constitutes a main flow path through which the coolant 1 flows with a relatively fast velocity. On the other hand, in the inter-thermal insulator flow path 322 provided below the coolant outlet nozzle 17, the coolant 1 flows with a slower velocity than in the main flow path. Also, the radial connection portion 7′ is located at a central position of the flow path 322, 321.